Method of producing purified stabilized sodium hypochlorite



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United States Patent SODIUM HYPOCHLORITE METHOD on PRODUCING PURIF'IED STA'BHQITZED LarryJ. Bartom San Leandro, Calif, assignor, by inesne assignments, tofThe' Clorox'Company, Cincinnati, Ohio, :1 corporationofohio No Drawing. AppIicatiUn Septeniber IS, I956 Serial No.61'0,667

3 Claims. "(01. 23-86) This invention relates "to hypochloritesolutions and -more particularly to -'a-'purified-stabilized'alkali metal hypochlorite solution, especially a sodium hydrochlorite solution, and :to :amethod of producing same.

Sodium hypochlorite solutions have wide applicability as disinfectants, germicides and bleaching,'stain removal and deodorizin'g agents. The commercial method of pro ducing such solutions is by gassing an a'queous'solution of commercial caustic soda or sodium hydroxide with liquid chlorine, "chlorine gas, or a combination of the two. Such solutions are'then allowed to clarify by settling, after which they are" packed in various sized bottles for the'grocers"shelves.

One of the serious problems facing the manufacturer of such -a product isthat of instability of the sodium hypochlor'ite solution where there is a continuous loss of strength or available chlorine.

7 Because of the'cornmericalcaus'tic employed in "the manufacture of such solutions, they contain, in a dissolved state, varying minute amounts of different foreign metals or metallic salts, which act as catalysts "intensifying the speed of such'brea'kdown. This "is so 'because commercial'ca'u'stic soda which generally comprises 50% to 73% by weight sodium hydroxide together with "a minor amount of about 1% to 3% by weight of sodiumcarbonate, is manufactured in dilute concentrations, then concentrated by means of evaporation in suchyessels as carbon'steel,

"stainless steel, Monel metal, nickel or nickel alloys.

As the caustic'soda is heldin'these vessels under elevated ternperatufeflit g'radual'lypicks up "minute "amounts of such foreign metals "ortheirtn'etallic salts, which "may be classified underthe he'ading Catalytic acting? The'se metals or their salts are'istill retained in solution after the chlorinating operation has been completed and a sodiumhyp'och'lorite solution formed. 'The main group of such 'Catalytic acting? metals -'or their salts, comprises copper, chromium, nickel, cobalt, iron, manganese,

zirconium 'and'vanadi'um. These metals or their salts are held in a dissolved condition in the commercial caustic soda "solutionas it comes from the manufacturer and are found ingrea'ter amount as the concentration of such caustic soda increases in thesolution.

It has been found that very'minute quantities of such Catalytic acting "metals "in 'solution have considerable effect as catalytic agents. In fact, it has been found with these metals that quantities as low as 020 part per million exercise a very deleterious effect upon the stability of sodium hypochlorite solutions, and also appreciably retard their speed of clarification.

Another problem facing the manufacturer is the. speed at which such sodium-hypochlorite solutions will settle out to complete clarity. The-length of time necessary to settle requires longer operating periods and a greater number of available tanks, with their attendant costly floor space, in which to store the solution while clarifying. These naturally add to the cost o'f'manufacturc; particularlyfwlren it'is-"considered that such tanks must be lined wi tlrth'e"customarily employed materials, such tate.

2,918,351 Patented Dec. 22, 1959 as rubber or pla'stics, inert to "the action of sodium hy- "po'clilor-ite. The life of these materials is relatively short and costly maintenance is required for such tanks.

-When a sodiumhypochlorite solution is being manufacture d,f'there is an appreciable amount of precipitate "fo'rmed. This'precipitate is in a'very highly dispersed or s'enrico'l-loidalcondition and such precipitate continues to form over approximately the first seventy-two hours of "settling. As experience has been gained in the manu- "facture and handling 'of such solutions, it has been observed that a very peculiar situation exists in that a sodium hypochlorite solution may be allowed to settle tothe point at which there is apparently complete clarity 'of the solution and complete freedom from any precipi- H'o'we'ver, after such a -solution has been bottled andhas stood for approximately seventy-two hours or more, it has been noticed that a very light precipitate has formed. Inasmuch as'such solutions find wide use forpersonal, hospital and surgical uses, the presence of such a precipitate is most undesirable. This precipitate "is composed of'fn'inor amounts of metallic oxides which have oxidized to an insoluble form due to the combination with the sodium hypochlorite and that group of metallics'alt precipitates which formby beingconverted to insoluble carbonates during the process of reaction.

"It would be surmised, according to present chemical kn'owledge.'that these insoluble carbonate-forming metals woiild'bel precipiated as the carbonates during the process 30 of chlorination. as during such reaction there is a certain amount of sodium carbonate inherently contained within thccommercial caustic, and'the reaction of carbon dioxide-'fromthe air upon the caustic solution during such chlorination further increases the percentage of carbonate withinsuchsolut-ion. While theoretically this maybe true, in practice it has been found that these salts either arein the solution in some complex form, as for instance, a sodium calcium salt or it may be that under normal conditions their solubility is such that they will remainin solution without interacting with the carbonate C 0 radical and hence do not combine to form an insoluble carbonate capable ofprecipitating out and settling. It also may be that theyare in a semi-stable condition such that even an excess of the carbonate (CO radical will not-combine withthe'complex salts. Various tests have been made using additions of larg quantities of sodium carbonate and/or large quantities For instance, a solution formed by the addition of grams of solid carbon dioxide to 40 liters of a 5.5

,percent by weight'aqueoussodium hypochlorite solution analyzed 28 percent by weight sodium bicarbonate with apH of'9.0; the same solution and amount thereof formed the use of 80 grams of carbon dioxide gas analyzed the same with the same pH; whereas, the sameamo'unt of such solution of the same analysis of .28.percent by weight sodium bicarbonate formed by the addition of sodium bicarbonate had a pH of 9.6. In addition,-it was found that it was very difiicult to dissolve thesodium bicarbonate, prolonging the process of manufacture to a point'not compatible with efiiciency.

. These metals or their salts which normally precipitate out very slowly "in the manufacture of a sodium hy- 'pochlorite solution may be classed under the general heading of Delayed precipitation?" metals. 'They comprise minute amounts of metals or their salts also inherent 1 I to and dissolved in manufactured caustic soda besides the aforementioned Catalytic acting metals, such :as calcium, magnesium, barium, strontium, aluminum, boron, I I

soda to theproper Baum for chlorination, suchas cal- -cium', magnesium, barium, strontiumpaluminum, boron Iron and manganese metals or their inherent and. silver.

salts are alsodissolved in such water as well as in the I commercialcaustic; I I I I I I y From the preceding, it is seen'thereare two groups of I metals ortheir salts which occur as foreign components andin minute quantities in thecommercial manufacture of a sodium hypochlorite solution and which present y problems in the commercial production of a stable, sub- 1 stantially foreign metal I free and consequently clear, un-

cloudy sodium hypochlorite solution from which i such i v foreign metallic components are quickly eliminated. They are the aforementionedCatalytic acting and Delayed.

recipitation metals; .and it will be noted that some of I I P these metals, such as iron and manganese occur in both groups.

The present invention has as its objects, 'among'others, i

the provision of an improved method for overcoming such problems byv substantially. completely eliminating such metals in'a simple, quick and safemanner and also eliminating the alkalinity imparted to the solution by su'chmetals to thereby increase activity ofthe solution,

and the provision of an improved stable, clear alkali metal hypochlorite solution.

' Fora general summary of ho'w such objects are accomplished the following: factors: should :be considered.

As previously related, the activity (rate at which oxida-' .tion occursby evolution of available chlorine") of a hypochlorite solution increases with: decreasein pH or alkalinity. However, if insufficiently alkaline the soluline and very stable, as is pointed out in applicants and assignees Patent No. 2,170,108, dated August'22, 1939. However, upon continued chlorination, the sodium carbonate present will react with the chlorine resulting in formation of sodium bicarbonate; and both the carbonate and the bicarbonate will exist simultaneously but as chlorination proceeds, the carbonate content will decrease and the bicarbonate content will increase with gradient decrease in alkalinity to the point where the solution will spontaneously disintegrate with the force of an explosion.

This is due to the fact that chlorination of sodium carbonate and sodium bicarbonate results in formation of hypochlorous and hydrochloric acids imparting to the solution a relatively strong acid. Thus, in the manufacture of sodium hypochlorite, it is commercially infeasible to reduce the pH of a caustic soda solution by chlorination, much beyond the point at which all the sodium hydroxide has been chlorinated, as the changes that occur when the sodium carbonate commences to react with the chlorine, with resultant formation of hypochlorous acid '40 tion will slowly lose its strength or even spontaneously oxide for chlorine to bring the solution'down to a rela+ I tively low pH at which it has such characteristics as to effectv rapid precipitation ofthe: aforementioned undesirable foreign metallic impurities. v

Atleast sufficient carbon dioxide should The added in substantially, molar proportions to, react with all sodium hydroxide, if present inthe 'solutiomand substantially all sodium carbonate present, to form sodium bicarbonate as the only stabilizing alkaline substance in the solution.

At such point, the'solution will rapidly clear itselfof the resultant precipitated foreign metallic impurities; and although having a relatively low pH which cannot safely be obtained by direct chlorinationofthe 'solutionyit' will I I be sufiiciently stable. Greater stability for shelf lifeand I bottling purposes can, beimparted to the solution by adding sodium hydroxide to bringthe: solution'up to a I desired pH.

I In greaterdetail,'under'normad chlorination, of a com ,mercial' aqueous sodium hydroxide solution, thefollow ing reactio n occurs: H V H ,1

' zisaon+c1,mascot-Frag y-huo I 3 Usually in commercial practice, this reaction will be stopped atthe point wherethe solution contains a minute 'amount;ofresidual" sodium hydroxide approaching zero as disclosed intheaforementioned Patent No. 2,170,108, tip to an excess ofpossibly .O.50.p er ce nt If the chlorinationproceedsto the point Ya'tfwhich; there is substantially I 7 'zero sodium hydroxide, ,it will be, an alkaline solution i gaining such alkalinity from the'contained sodium carbonate in the caustic,solutionfhAt this point, solutions 'icontaining from ,4.0 to 10.0 percent by weight (all otherpercentages hereinafter mentioned are by weight) sodium hypohloiitewillhavke a pl l'i'n the range of 11.3.to;11.8 I

and usually about 11.5. Apparentlythe pH is. controlled 1 ,byjalkalinity alone, with wide diiferences of sodium hypochlorite having} little or no effect. If; the, chlorination is carriedfurther in such solutions, the sodium carbonate will be reacted, on to the pointat .whichthesolutions will :containYboth' sodium carbonate and sodium bicarbonate.

When the sodium carbonate commences to react in the process, the pH will, drop in the range of approximately 11.0 to 11.3. r As the reaction proceeds, it is intensified by continued reaction of the sodium carbonate with the chlorine resulting in decreasing amounts of sodium carbonate, with inaccording to the following reactions -z a wZNaCl-l-ZHOCKZHCl-l-OQ It hasfbeen found in practice that by exercising extreme caution and proceeding slowly, this reaction may :creasing amounts of sodiumhicarbonate being formed be carried to the point at which the solution will contain as much as .05 to .09 percent sodiumbicarb'onate plus .17

to .20 sodium carbonatewith 'a pH of from 9,7 to 10.0.

From-the point at which the sodium hydroxide reached zero, to the mentioned point where the solution contains .05 to .09 percentso dium bicarbonate, maybe classed as the Precipitant stagefij- Duringthis state, a small amount of iron and manganese contained in the solution in a soluble form-will be oxidized and will drop out as an insoluble precipitate. In addition, a small part of the metals capin their insoluble oxideorcarbo nate' stite.

; thefsolution reaches the periodjof ultimate chlorination, namely,.after the sodium carbonate has completely reactedwith the chlorine, leaving only the sodium bicarbonate available for reaction, according to the reaction.

act-e351 ZHQCQg-l-ZHOCKZHCl-l-O) "temperatures increase rapidly, and wit-h the decrease in alkalinity and the increase in temperature, such solution will spontaneously disintegrate due to formation of hypochlorous acid (HOCl) which' breaks upirito hydrochloric -=acid with evolution of oxygen, as ind-icatedin the precedingequation. This is a most dangero-ussituation in that as the solution spontaneously disintegrates, all of the *chlorine contained as sodium hypochlorite will be released and pass off into the atmosphere in a'few seconds in tremendous quantities. It'is obvious that'this release 0f hot chlorine gas is highly-disadvantageous in that c-hlorine, being a highlyirritant and poisonous gas, could seriously affect anyone'in the vicinitycoming in contact with same.

In this invention, a procedure-is providedfor producing not only the above mentioned Precipitant stage but also forcing the solution to a point wherein such a solution will contain'no sodium hydroxideand no sodium carbonate but will still be sufliciently alkalineand consequently sufiiciently stable so that it will not disintegrate. The alkalinity will be conferred to the solution by its content 'of sodium bicarbonate alone. Furthermore, the alkalinity 'of-sucha solution can be lowered to an' Ultimate point where a-solution containing from approximately 4.0 up to 10.0 percent sodium hypochlorite willcontain sodium bicarbonate as its only alkaline component and have a pH of 9.3 to 9.5.

Further, this can be done With absolutely no danger of over chlorinating to the point of spontaneous disinteg ration, with temperature of the solution actually dropping instead of increasing. This is accomplished by, forming in the solution the weak carbonic acid instead of the strong hypochlorous and hydrochloric acids, by addition in the solution of carbon dioxide, desirably solid carbon dioxide, instead of chlorine in the latter stages of the procedure. The result of this is an appreciable saving in the cost of lost chlorine due to the'decreased breakdown of sodium hypochlorite at the higher temperatures.

A further advantage is that sodium hypochlorite solu- "tions can be produced directly, containing up to 10.0 percent sodium hypochlorite with no necessity of precooling the sodium hydroxide solution and no necessity of using cooling during the course of manufacture. Furthermore, such procedure will eliminate substantially all of the above-described metals or their salts from the solution.

- Hence, there is no necessity for using any type of water softening treatment for the water used in preparing the initial sodium hydroxide solution.

' At the above mentioned Ultimate point where the solution contains only sodium bicarbonate as its only alkaline component, and has a pH of 9.3to 9.5, the solution'is' so active chemically that it has characteristics completely unthought of previously. Substituting carbon "dioxide'for chlorine during the Iaststages of-the manufacturing process is represented by the reactions:

-At this-point, the high oxidizing values ofsuch a solution are so strong that substantially all of the dissolved metals or metallic salts are'oxi'dized'toan insoluble state and precipitated from the solution. At-the same time, the carbonation activity is so great'that all of the insoluble I carbonate-forming metals are so converted' and will precipitate out in such form. It is believed that this action is caused by the fact that the carbon dioxide, being in a concentrated and active state, combines with the water -of the solution to produce a small amount of carbonic 'acid,and it is this carbonic acid which is sufficiently strong "and active enough to convert the complex salts of these :metals into their carbonates but not strong enough in aacidity. to cause spontaneousdisintegration as'would be ;trueif;hypochlorous and hydrochloric acids were present.

.hypochlorite solution wereplaced .in carboys. This solution was chlorinated in a conventional manner to the point where it contained approximately 5.50 percent so-.

dium hypochlorite, .03 percent sodium hydroxide, and .11 percent sodium carbonate. -At this state of the test all of these carboys contained solution having a precipitate as would normally be found in such a regularly chlorinated solution; such precipitate being in a finely dispersed or semicolloidal condition and imparting a high degree of cloudiness to the solution.

One of these carboys was maintained as a control in each series of tests, and allowed to settle with no further treatment. Other carboys weregiven a further treatment adding in the first twenty grams of carbon dioxide and increasing in each of the others by steps of twenty grams each to the point where one hundred and twenty grams were added to the last carboy. Within a matter of minutes, it was noticed that in those carboys which had been treated with carbon dioxide the precipitate had rapidly changed to a heavily flocculated condition and at the end of approximately one-half hour, such. precipitate was beginning to settle.

At the end of two hours such settling was very apparent. The solutions in all of such carboyswere allowed to settle to absolute clarity. The carbondioxide treated solutions reached this point in from four to :six hours, while the control solutions required more than twenty-four hours, and in some instancesrequired as high as seventy-two hours. Aftersuch settling to absolute clarity, the supernatant liquid of the various' solutions was decanted off as far as possible; the'balance of the solutions then being filtered and the precipitates recovered. These precipitates were then dried and weighed, and it was found that where the carbon dioxide was used, these precipitates gained in total weight, confirming-the appearance as determined by visual observation.

These increased weights definitely established tha metallic compounds were being precipitated from the solutions and differed radically from that precipitate obtained from the controls. "as the amount of such precipitates increased, their color It was further found that darkened, showing definitely that increased amounts of metallic oxide had been precipitated, which again had not occurred in the controls. These precipitates, including those from the controls, were then placed under spectrographic analysis, which definitely showed the presence of metals appearing in the carbon dioxide treated samples which were not shown in the control samples. Further, spectroscopic study of the precipitates from the carbonated solutions showed the presence in appreciable quantity of all of those metals previously mentioned as being undesirable in the finishedsolution.

Also, portions of the dried precipitates from the carbon dioxide treated samples were placed under X-ray diffraction tests, which again showed the presence of a number of difiraction lines not appearing in the control samples. Theselines indicated the presence of additional compounds.

As was pointed. out previously, a further problem facing the manufacturer is how to develop a hypochlorite solutionhaving the lowest possible pH and still have the required stability for a commercial bottled product. It is well known in the art that as the pH of a sodium hypochlorite solution is lowered, its speed of action is intensified and its characteristics as a germicidal solution are greatly enhanced.

As a result, such a solution will be one considerably improved over existing sodium hypochlorite solutions as a disinfecting agent. This is particularly important today with the increased use of automatic Washing machines having a definite time cycle for their washing operation. The use of a faster acting sodium hypochlorite solution means that the housewife may be sure of having a better disinfected wash than she would have if the non-improved types of sodium hypochlorite solutions were used.

As previously mentioned, the process of this invention enables production of a sodium hypochlorite solution containing only sodium bicarbonate as its alkalizing component and having a pH as low as 9.3, but generally in the range of 9.3 to 9.5. This represents the ultimate lowering of alkalinity which may be obtained by the use of carbon dioxide. It has beenfound that if additional amounts of carbon dioxide are added to the solution, there is no apparent effect on pH. It appears to be that any carbon dioxide added in addition to that necessary to reach the above Ultimate point of a pH range of 9.3 to 9.5, is dissipated without further beneficial chemical effect. Such additional carbon dioxide might even prove disadvantageous in that the excess carbon dioxide above that necessary for reacting with all sodium hydroxide if present, and all sodium carbonate to convert them to the bicarbonate and thus result in complete metallic combination and precipitation, will in the course of time, react with the sodium hypochlorite, causing an unnecessary loss of available chlorine due to the formation of the highly unstable hypochlorous acid, according to the reaction In commercial operations, for example, the Ultimate point will be reached when approximately one gram of carbon dioxide has been added per liter of an aproximately 5.5 percent aqueous sodium hypochlorite solution containing approximately .01 percent sodium hydroxide, resulting from chlorination of approximately 70 grams of sodium hydroxide, and will vary slightly in amount as such sodium hydroxide is either slightly raised or lowered according to the reaction CO2 =NaHCO3 The chlorination of the caustic solution could be terminated at a point where an excessive amount of the caustic is still present, for example, 0.5 percent but then considerably more carbon dioxide would have to be added to react with the excess sodium hydroxide and reduce the alkalinity to the Ultimate point where substantially only sodium bicarbonate imparts alkalinity to the solution but this is not practical. Also, the chlorination can be effected to a point where all the sodium hydroxide has been consumed and some of the sodium carbonate has been reacted with chlorine, but this requires too careful control in order to avoid spontaneous disintegration. Therefore, it is desirable in commercial operations to chlorinate to the point at which there is only a slight percent of up to .04 percent sodium hydroxide in the solution, and then substitute the carbon dioxide for the chlorine in the procedure to arrive at the above mentioned Ultimate point.

In any event, irrespective of the desired end point to which the solution is chlorinated above the point of spontaneous disintegration thereof, it is only necessary in order to arrive at the aforementioned Ultimate point, to add at least sufficient carbon dioxide in substantially molar proportions to convert all sodium hydroxide, if present, and all the sodium carbonate to sodium bicarbonate. The amount of carbon dioxide required for this purpose can be readily calculated by determining the amount of sodium hydroxide, if any, present in the solution, and the amount of sodium carbonate present.

In commercial chlorination of a caustic soda solution, the operator can tell when the solution approaches about .2% to .3% sodium hydroxide because at such point the solution changes from a cloudy to a golden clear. One

can then analyze the amount of sodium hydroxide present and determine how much more chlorine is required to bring the sodium hydroxide content to substantially zero. At such point, the amount of sodium hydroxide can be determined in the usual manner by titration with hydrochloric acid with phenolphthalein as an indicator, and

of the contained sodium bicarbonate.

chloricqacid: with methyl orange or tetrabromphenolsulfonphthalein as an indicator. The amount of sodium carbonate can then be ascertained by subtraction ofthe two determinations. From these results, the amount of carbon dioxide to be added to arrive at the Ultimate point can be readily calculated for any given solution.

At the Ultimate point" the hypochlorite solution is relatively unstable and if allowed to stand too long in this state, results in arelatively rapid breakdown of the sodium hypochlorite to a point where a solution of a given concentration would lose approximately fifty percent of its available chlorine in. about three days. However, such a solution may be substantially permanently stabilized by the addition of sodium hydroxide up to a desired analysis, pointed out later, without havinglost any appreciable amount of available chlorine due to such period of standing in, its relatively unstable state but such correction should be made as quickly as possible.

After such addition of. sodium hydroxide, the solution will still be completely or substantially free from all of those metallic components which act catalytically to destroy stability, and will be completely or substantially free of all of those other metallic components which delay substantially complete and immediate precipitation and retard rapid clarification.

It has been further found that in the addition of such sodium hydroxide for purposes of stabilization, the solution when brought back to a given sodium hydroxide content, for example, .01% by weight, will have greater stability than the same solution chlorinated directly to such sodium hydroxide content. Also, lower amounts of sodium hydroxide are required than have heretofore been found necessary in former known types of a sodium hypochlorite solution, and still have stability better than that found in the previously existing types of such solutions. This is because of the elimination of the unstabilizing buffering metal impurities by the method of this invention and the reduction of alkalinity which would otherwise be imparted to the solution by these metal impurities.

Although when sodium hydroxide is added to stabilize the solution for long shelf life, it is preferred to bring the solution back to a slight sodium hydroxide content approaching zero, this is not necessary, because solutions of very high stability can be obtained without the presence of any free sodium hydroxide so long as the presence of too high a percentage of sodium bicarbonate is obviated. Tests have shown that stability can be conferred to such caustic-free solution if the amounts of contained sodium carbonate are not allowed to go below twenty times that For example, a hydrochlorite solution containing approximately 5.5 percent sodium hypochlorite, .45 to .48 percent sodium carbonate, and not more than .02 percent sodium bicarbonate, and having a pH of 11.0 to 11.3 will be stable. Such a solution will be very active and efficient as a disinfectant and will be very fast in its germ-killing action due to its lower pH.

From the preceding, it is seen that there are various end points at which the chlorination of the caustic solution can be terminated before the carbon dioxide is substituted for the chlorine in the latter stages. However, in all cases, chlorination should be terminated while the solution has an alkalinity suificient to preclude spontaneous disintegration thereof.

Thus, in the operation of this invention, a solution of sodium hypochlorite can be prepared in the desired amount and to the desired analysis of contained sodium hypochlorite. During the chlorination of such solution, the chlorination may be stopped at the point wherein the solution will'contain from .01 to .04 percent sodium hydroxide, at which point the carbon dioxide may be added. While the chlorination could be stopped at any suitable point above these amounts of sodium hydroxide,

I ihgnic acid solution a'very fine catharti asi ma be P e red brew n ga h -nipx d 9 ats nd ad d o th hy achl t e sslution v n-th tarmh b en found n P ti e tha i z i e 'y d r bl tqa the a on-z i xi e in th scl d t ra o d a diox m. in fi ty und-parswa ka e desirable. It is believed that inthe immediate vicinity of each of these solid carbon dioxide lumps. there. is an intensified local action of some unknown nature, probably jdue to the great temperature difference between the carbon dioxide and the, solution, which resi lts inimparting to the solution the maximum characteristics desired in a rapid and positive manner.

While it has been mentioned that carbondioxidein .Lthe gaseous form may also be used, therearecertain mechanics of operation which are undesirable, Con- .siderable storage facilitiesare: required for the gas; it ..is hard to obtain accurately weighedamountstdt fi to. .1 ;he slowness with which the gas must be added, there is ad- ..ditional time requiredto complete the operation. Be-

cause of this slow addition .of..gas, there is..praetically no stirring effect developed andnone. of the advantages ,of cooling the solution.

Similar disadvantages are found with the use of .carbonic acid solution. This requires special equipment to prepare which increases initial costs and requires upkeep and maintenance. Further, there is a duplication of steps that carbon dioxide must be added to-water. -tg-produce isueh a solution.

It has jfur'therbeen found that hygthe use Qfthis; carre cipitatejlis 'formed .Whichihas a tendency to float 'on' t up of the selution, ..does not result in good'coagulatign, does ;no t';-Qg ive as rapid settling characteristics. It"is"further necessary to initially prepare the sodium hypochlorite at higher concentrations to compensate for this dilution which is also undesirable. It has also been found that solutions prepared in such a manner may be lowered to a pH of 9.3 but do not build up sodium bicarbonate to the desired amount; it actually appears that the carbonic acid attacks the sodium hypochlorite with a very rapid breakdown of available chlorine.

With the use of liquid carbon dioxide, similar difficulties are found in that it is very difficult to actually bring the liquid carbon dioxide to the sodium hypo chlorite solution without its first breaking to a gas or to a finely flaked solid condition. It is diflicult to add exact amounts, and the benefits of stirring are not as favorable as with the use of solid carbon dioxide.

The following examples are illustrative of the invention.

Example I To a conventional chlorinating tank which is lined with rubber, hard rubber, or any of the plastic materials which are inert to sodium hypochlorite solutions, one thousand and fifty gallons of a solution of commercial .bl cks: and may be obtained a sliced formwherein .10 g anstic soda :at 150.2 .Baum (approximately fifty. percent NaQHhy eight) areaddedrsuch solution being atroOm .temperature. To this is. added ten thousand gallons :of Water at roomtemperature, which does not havetoibe either pretreated or precooled. After mixing, such solution will have a specific gravity of approximately 1.069 .at.80 F. This-solution is now chlorinated in a conven- .tional' manner, by the introduction into thesolutionrof gaseous chlorine, but which may be liquid if so desired, to .apoint at which the amount of sodium hydroxidein thesolution approaches Zero, namely, approximately .01 to .02 percent sodium hydroxide as determined by standard methods .of chemical analysis previously pointed out.

.At this point, the solution will have swelled to where it will comprise eleven thousand three hundred .and fifty gallons at 5.28 percent available chlorine with atemperature of about 100F. :and-a pH of 11.5 011.8 and .have a specific gravity of 1.070 at 100 "To this solution is :now. added one hundred and ten pounds of olid ..carbon dioxide in sliced form of about oneinch ,cubes. Such carbon dioxide is allowed to completely dissipate itself which will be in about 3 to 5 minutes 'during which time the solution may be further mixed by means of air; and the resultant temperature will be [about 95.F.

.Such. solution will now analyze zero sodium hydroxide and zero sodium carbonate and approximately .26 to .30

.percent sodium bicarbonate,-with a pH of approximately 9.3 to 95. 'If not at this analysis, small corrective additions of carbon dioxide may be made. This solution should now be corrected as promptly as possible, the sooner the better, by the addition of one hundred and seventy-five pounds of sodium hydroxide as represented by twenty-eight gallons of ;percent sodium hydroxide solution. However, the solution can be allowed to stand for up to 120 't o"30 minutes without appreciable loss of h 0ri Thefsolutionshould then be thoroughly mixed for ten to fifteen minutes by air agitation, at which time'it is chemically checked and then may be pumped to a proper settling tank. The resultant final solution will now analyze approximately 5.26 percent available chlorine 0.0% sodium'hydroxide, and .44 to .48 percent sodium carbonate with a pH of from 11.3 to 11.8.

- There may be slight deviations from this analysis in that such-solution might contain as high as .01 to .03 percent sodium hydroxide in addition to 'the sodium carbonateor might go as low in alkalinity as to contain from ,01 to .02 percent sodium bicarbonatein addition to the sodium carbonate. .Such a solution will clarify 'completely to substantial clearness within a matter of three or four hours, with resultant precipitation of the metallic impurities to the bottom of the tank, at which time the clear solution may be bottled by any standard procedure.

Example II To a conventional chlorinating tank of the type described in Example I, 2,500 gallons of a solution of commercial caustic soda at 31.5 Baum (approximately 25 percent NaOH by weight) are added, such solution being at F. To this is aded 10,000 gallons of water at room temperature which does not have to be either pretreated or precooled. After mixing, such solution has a specific gravity of approximately 1.071 at 91 F. This solution is now chlorinated as in Example I to a point at which the amount of sodium hydroxide in the solution is completely consumed by the reaction; and the solution con-' tains, upon determination by standard methods of chemical analysis previously pointed out, 0.20 percent sodium carbonate and 0.06 percent sodium bicarbonate.

At this point the solution will have swelled to where it will comprise 14,150 gallons at 5.78 percent available chlorine with a temperature of about 118 F. and a pH of 9.7 to 10.0. To this solution is now added pounds .cubes. Such carbon dioxide is allowed to completely dissipate itself, which will take from about 3 to 5 minutes, during which time the solution may be further mixed by means of air, and the resultant temperature will be about 115 F.

Such solution will now analyze zero sodium hydroxide and zero sodium carbonate and approximately 0.28 to 0.32 percent sodium bicarbonate, with a pH of, approximately 9.3 to 9.5. If not at this analysis, small corrective additions of carbon dioxide may be made as in Example I. Thissolution should now be corrected as promptly as possible, as in Example I, by addition of 190 pounds of sodium hydroxide as represented by about 59 gallons of '25 percent sodium hydroxide solution. As in Example I,

the solution can be allowed to stand for up to20 to 30 minutes before the addition of the sodiurn hydroxidewithout appreciable loss of chlorine.

The solution should then be thoroughly mixed for to minutes by air agitation at which time it is chemically checked and then pumped to a proper settling tank. The resultant final solution now analyzes about 5.75 percent available chlorine, 0.0 percent sodium hydroxide, and .44 to .48 sodium carbonate, with a pH of 11.3 to 11.7.

There may be slight deviations from this analysis as described in Example I; and such solution will also clarify completely to substantial clearness in the time described in Example I, and then bottled.

Although the invention is particularly applicable for the manufacture of a sodium hypochlorite solution, other alkali metal hypochlorites, such as potassium, can also be produced thereby with the same advantages.

I claim:

1. In the method of producing'an aqueous sodium hypochlorite solution wherein sodium hydroxide containing sodium carbonate is chlorinated to eiiect a reaction with said sodium hydroxide resulting in formation of said hypochlorite and wherein continued chlorination beyond the point at which the sodium hydroxide is reacted results in reaction of chlorine with the sodium carbonate forniing increasing amounts of sodium bicarbonate withtconsequent decreasing amounts of the carbonate, the steps of terminating the chlorination at a predetermined point at which the solution has an alkalinity sufficient to preclude spontaneous disintegration thereof, efiecting substantially complete precipitation of foreign metallic components in the solution including metallic components thatcatalyze decomposition of such hypochlorite, by adding thereto carbon dioxide in an amount to combine with any sodium hydroxide present in the solution and all sodium carbonate therein to produce sodium bicarbonate, and enhancing 12 stabilization of the solution by addition of sodium hydroxide.

2. In the method of producing an aqueous sodiumhy- I pochlorite solution wherein sodium hydroxide containing sodium carbonate is chlorinated to 'etfect a reaction with said sodium hydroxide resulting in formation :of said hypochlorite and wherein continued chlorination beyond consequent decreasing amounts of the carbonate, the steps of terminating the chlorination when the sodium hydroxide content approaches zero, efiecting'substantially complete precipitation of foreign metallic components inthe solution-includingmetallic"components that catalyze decomposition of such'hypochlorite, by adding thereto solid carbon dioxide in an amountto combine with all sodium hydroxide and all sodium carbonate to produce sodium bicarbonate, and enhancing stabilization of the solution by addition of sodium hydroxide. 3. In the method of' producing an aqueous sodium hypochlorite solution wherein sodium hydroxide containing sodium carbonate is chlorinated to effect a reaction with said sodium hydroxide resulting in formation of said hypochlorite and wherein continued chlorination beyond the point at which the sodium hydroxide is reacted results in reaction of chlorine with the sodium carbonate forming increasing amounts of sodium bicarbonate with consequent decreasing amounts of the carbonate, the steps of terminating the chlorination at a predetermined point at which the solution has an alkalinity suflicient to preclude spontaneous disintegration thereof, effecting substantially References Cited in the file of this patent UNITED STATES PATENTS 1,023,287 Wilsing Apr. 16, 1912 1,483,463 MacMillan Feb. 12, 1924 1,883,649 Engberg Oct. 18, 1932 2,170,108 Barton Aug. 22, 1939 2,288,841 Ritter July 7, 1942 2,610,905

Hinshaw Sept. 16, 1952 mu... w

I a a UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 2,918,351 December 22, 1959 Larry Ja Barton It is hereby certified that error appears in the printed specification of the above numbered patent requiring correct-ion and that the said Letters Patent should read as corrected below.

Column 4, line 12, for "safety" read safel line '71, for "stite reed state -----5 column 8, line 53., for "hydrochlorite" read hy'pochlor=- its column 10, line 62, for "aded" read added Signed and sealed this 31st day of May 1960,

Attest:

KARL H, AXLINE ROBERT C. WATSON Attcsting Oflicer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N00 2,918,351 December 22, 1959 Larry 5., Barton It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should readas corrected below.

Column 4, line 12, for "safetgfl read safel line '71, for "stite" read state column 8, line 53, for "hydrochlorite" read hypochlorite column 10, line 62, for "aded" read added Signed and sealed this 31st day of May 1960,

(SEAL) Attest:

KARL Hg AXLINE ROBERT C. WATSON Commissioner of Patents Attesting Officer 

1. IN THE METHOD OF PRODUCTING AN AQUEOUS SODIUM HYPOCHLORITE SOLUTION WHEREIN SODIUM HYDROXIDE CONTAINING SODIUM CARBONATE IS CHLORINATED TO EFFECT A REACTION WITH SAID SODIUM HYDROXIDE RESULTING IN FORMATION OF SAID HYPOCHLORITE AND WHEREIN CONTINUED CHLORINATION BEYOND THE POINT AT WHICH THE SODIUM HYDROXIDE IS REACTED RESULTS IN REACTION OF CHLORIDE WITH THE SODIUM CARBONATE FORMING INCREASING AMOUNTS OF SODIUM BICARBONATE WITH CONSEQUENT DECREASING AMOUNTS OF THE CARBONATE, THE STEPS OF TERMINATING THE CHLORINATION AT A PREDETERMINED POINT AT WHICH THE SOLUTION HAS AN ALKALINITY SUFFICIENT TO PRECLUDE SPONTANEOUS DISINTERGRATION THEREOF, EFFECTING SUNSTANTIALLY COMPLETE PRECIPITATION OF FOREIGN METALLIC COMPONENTS IN THE SOLUTION INCLUDING METALLIC COMPONENTS THAT CATALYZE DECOMPOSITION OF SUCH HYPROCHLORITE, BY ADDING THERETO CARBON DIOXIDE IN AN AMOUNT TO COMBINE WITH ANY SODIUM HYDROXIDE PRESENT IN THE SOLUTION AND ALL SODIUM CARBONATE THEREIN TO PRODUCE SODIUM BICARBONATE, AND ENHANCING STABILIZATION OF THE SOLUTION BY ADDITION OF SODIUM HYDROXIDE. 